1. Field of the Invention
The present invention relates, in general, to a backing plate for a brake shoe for use in a trolley car braking system and, more particularly, to a multi-functional metal insert for use with a backing plate assembly in the formation of composite brake shoes for use in trolley car braking systems.
2. Description of Related Art
Milan type trolley cars, which are mass-transportation systems common in several cities, such as San Francisco, Calif., currently use cast-iron brake shoes in their braking systems. Examples of these types of brake shoes, generally indicated as 10, are shown in FIGS. 1A and 1B. These brake shoes include a U-shaped groove 12 that is used to help align the brake shoes against the vehicle's wheel (not shown) during braking by guiding the brake shoe flanges 14, 16, located at the outer ends of the brake shoe 10 against the wheel flange. The friction surface 18 which contacts the wheel is typically thicker at one end 20 than at an opposite end 22 thereof. Due to the non-symmetrical shape and thickness of this type brake shoe; i.e., wherein flange 14 is larger in size than flange 16 and differing thicknesses 20, 22 of the friction material, proper installation thereof requires a right hand and a left hand shoe. Presently, a mechanic performing the installation is relied upon to properly orient the brake shoes during installation in the vehicle.
Additionally, since these brake shoes are produced from cast iron material, as the brakes are applied, cast iron wear particles and dust contaminate the city streets where the trolley cars operate. Presently, considerable expense is incurred to periodically clean the cast iron residue from the city streets.
As shown in FIG. 2, composition friction material brake shoes, generally illustrated as 25, have been produced using metal backing plates 26. These types of brake shoes include a pair of side flanges 28, 29, located at opposite ends of the brake shoe 25, for alignment with the wheel flange (not shown) during braking to bring the composition friction material 30 into contact with the wheel surface (not shown).
FIG. 3 shows an example of the backing plate, generally indicated as 26, which may be used in the composition brake shoe 25 of FIG. 2. The backing plate includes the pair of U-shaped side flanges 28, 29. A metal insert 32 may be separately welded to a front surface 33 of the backing plate 26. A key bridge 34, which facilitates attachment of the brake shoe 25 to a brake head, may be separately welded onto a back surface 35 of the backing plate 26. U.S. Pat. No. 6,241,058 to Shute et al. shows another example of a brake shoe suitable for use in a railway vehicle. This type of brake shoe includes a backing plate having a first friction type composition material bonded to the backing plate and at least one discrete insert formed of a second friction type material molded into the first friction type material. These types of brake shoes include multiple processing/molding steps.